Refiners designed for the production of paper pulp are generally provided with a sensor arrangement of the magnetic type, that is positioned so that it is stationary in the stator with the end surface of the measuring head on a level with the surface of the grinding segment, for measuring the size of the grinding gap between the stator and the rotor.
A disadvantage of locating the sensor in the surface of the grinding segment is that the sensor is subjected to continual wear during operation. The tip of the sensor with the measuring head is worn down at the same rate as the grinding segment in the machine and the sensor must therefore be replaced when the wear has become so great that the quality of the produced pulp has deteriorated. A normal interval of time between replacements can, for example, be 16 weeks.
A conventional sensor arrangement comprises a sensor mounted in such way that it can be moved in an axial direction, for example by means of a roller screw, in a housing mounted permanently in the stator, for adjusting the arrangement during the calibration process or other functions, which sensor generally has a sensor body upon which a sensor tip is mounted, for example by welding, (at the end of which sensor tip the measuring head is located). The sensor body is normally attached in its housing by means of a screw connection that can be difficult to access and complicated to use and to lock. In order to replace a sensor, time-consuming dismantling of the sensor from the housing is therefore required, with the whole of the sensor including the sensor body and the tip of the sensor having to be replaced, which is labour-intensive and time-consuming.
A sensor of this type comprises a so-called AGS-sensor (adjustable gap sensor), that has been described previously in the Swedish patent document 520 322 from the same applicant and will therefore not be described in greater detail here.